Due to a low turnover rate of the horny cell layer and a decrease in the hyaluronic acid content, the aged skin is known to dry easily, to become easily roughened, dried, wrinkled, or loosened, and to decrease in thickness, resulting in impaired elasticity. In addition to aging, the above phenomena are considered to be caused by external factors such as exposure to ultraviolet rays, drying, and oxidation which cause a decrease in the function of epidermic cells and dermal fibroblasts, and decomposition of hyaluronic acid.
Cosmetics containing raw materials extracted from naturally occurring materials such as galenicals and chemically synthesized raw materials have been used to improve such aged skin. These cosmetics have been known to provide the skin with moisture and flexibility due to a moisturizing effect and a physicochemical effect of film formation and the like (Japanese Patent Applications Laid-open No. 6-279227 and No. 8-310934). Although the cosmetics are effective in improving a dry skin surface, the effect is temporary and the improvement is not essential.
For this reason, an effort of increasing hyaluronic acid production by promoting the metabolism function of the skin has been undertaken. Retinoic acid, for example, which is a metabolite of vitamin A and one of the bioactive isomers of vitamin A, is known to exhibit a variety of effects on the physiological activity of skin, such as an effect of promoting the growth of epidermic cells and fibroblasts (Tong P S et al., J. Invest. Dermatol. 94, 126–131, 1990, Varani J et al., J. Investig. Dermatol. Symp. Proc. 3, 57–60,1998), an effect of promoting hyaluronic acid production (Tammi R et al., J. Invest. Dermatol. 92, 326–332, 1989), a cornification improving effect (Wanner R et al., Arch. Dermatol. Res. 291, 346–353, 1999), an anti-psoriasis effect (Orfanos C E et al., Br. J. Dermatol. 88, 167–182, 1973), an anti-acne effect (Chalker D K et al., J. Am. Acad. Dermatol. 17, 251–254, 1987), an anti-wrinkle effect (Weiss J S et al., JAMA 259, 527–535, 1988, Tadaki T et al., Tohoku J. Exp. Med. 169, 131–139, 1993), and a photo-aged skin improving effect (Kligman A M et al., J. Am. Acad. Dermatol. 15, 836–859, 1986). Retinoic acid preparations have already been used as a photo-aged skin improver and a wrinkle improver in the US.
However, because retinoic acid is strongly irritating, the use of retinol, which is less irritating and less physiologically active, has been investigated. The use of retinol combined with various compounds to increase its physiological activity has also been investigated. A combined use of retinol with fatty acid amide (Japanese Patent Application Laid-open No. 08-301748) or dimethylimidazoline (Japanese Patent Application Laid-open No. 9-100211) is known to provide a synergistic effect on epidermic cell activation.
However, the conventional preparations containing vitamin A such as retinol, retinoic acid, or their derivatives cannot necessarily bring about a sufficient effect of activating epidermic cells or increasing hyaluronic acid production.
On the other hand, cosmetic compositions containing a bean extract such as soybean milk have been known and reported as having a moisture retention effect and a detergent effect (Japanese Patent Application Laid-open No. 62-36304 etc.). In addition, the use of fermented bean products in cosmetic compositions and the like, for example, products obtained by fermenting soybean milk with microorganisms of genus Rhizopus (Japanese Patent Application Laid-open No. 1-102011), genus Lactobacillus (Japanese Patent Application Laid-open No. 3-127713), or genus Bifidobacterium (Japanese Patent Application Laid-open No. 10-287540) have been known.
However, the effect of fermented bean products on epidermic cell activation and promotion of hyaluronic acid production when combined with other components has not been known at all.
The cosmetic compositions and the like containing fermented bean products may have a soybean odor, fermented odor, or irritating odor. The odor may be associated with a negative image of a rotted product and impart the user an unpleasant feeling. However, no effective method of decreasing the odor of fermented soybean products has been known.
An object of the present invention is to provide a skin preparation for external application exhibiting an effect of preventing and relieving skin roughness, a cornification improving effect, a moisturizing effect, and an effect of preventing and improving wrinkled or loosened skin by activating dermal cells and promoting production of hyaluronic acid, and therefore effective for retarding skin aging. The present invention also provides a process for producing the skin preparation.